1. Field of the Invention
The invention relates to a variable control device for use in regulating or throttling of relatively low flows of fluid, the device being a solid state device capable of electronically regulating relatively low flows throughout a moderate flow regime. The disclosures of a second application, entitled "Microvalve and Microthruster for Satellites and Methods of Making and Using the Same" and of related subject matter, Application Ser. No. 08/659,965, and also filed Jun. 7, 1996, and the provisional Application No. 60/000,106 on which it is based, filed Jun. 9, 1995, are both incorporated herein by reference.
2. The State of the Art
More specifically, it is known to use pressurized gas, such as Xenon, in small increments of flow to a thruster, using a so-called "thermothrottle" (a device of Russian origin) for each of a plurality of thrusters, wherein an elongate tube establishes a path for the requisite gas flow, and an electrical heater winding developed around and along the length of the tube is the means of controlling gas temperature and viscosity, and therefore flow rate, between inlet and outlet ends of the tube. But this is a cumbersome and expensive technique, involving problems of production reproducibility, and the dynamic range of flow control has its limitations. See, e.g., K. N. Kozubsky et al., "Plan and Status of the Development and Qualification Program for the Stationary Plasma Thruster", AIAA/SAE/ASME/ASEE 29th Joint Propulsion Conf. and Exhibit, Jun. 28-30, 1993, Monterey, Calif. (AIAA-93-1787) (the disclosure of which is incorporated herein by reference).
It is known from U.S. Pat. Nos. 4,604,090 and 4,715,852 to provide a miniature device for automated metering of insulin to certain diabetic patients. The device is surgically implanted in the body and establishes an elongate capillary path for controlled small flows of insulin within the body. The device is a consolidated prismatic assembly of laminations, of microchip proportions, wherein a flat silicon chip has a photo-etched surface characterized by an elongate single capillary groove, which may have a length of 10 to 15 inches, helically developed on approximately a half-inch square of a flat surface, between inlet and outlet ends, with a glass plate bonded to the grooved surface to complete the integrity of a single flow passage in the groove. The ambient environmental temperature is, of course, body heat, and there is no need for or suggestion of heat as a flow-control parameter. Furthermore, the fluid is a liquid and in the environment of these patents the device and/or the patient is intolerable of the presence of a gas in the liquid.